The present invention relates generally to clock and data recovery circuits and, more particularly, to clock and data recovery circuits for use with burst-mode signals.
Some communication systems transmit data serially over a channel such as a fiber optic cable. A transmitter in a serial communication system transmits data in a data signal with clocking information signaled implicitly in the timing of transitions in the data signal. A receiver recovers both clock and data from the data signal. The receiver may use many bit times of received data to begin recovering the clock and data. In addition, data may be preceded by or include preambles to aid in recovery of, for example, clock information. This initial locking time is generally of little concern in always-on communication systems, considering that the initial locking time is very short compared to the total time of data communication.
In some serial communication systems, data are grouped in bursts with no signaling between bursts, multiple transmitters may transmit data into the channel at different times, and each transmitter may have independent amplitude and timing characteristics. Since each burst of data may have an arbitrary phase, timing information from a prior burst is generally not of use in locking to a subsequent burst. In addition, as each burst may be relatively short, an initial locking time that was very short compared to the total time of data communication in an always-on communication system may be objectionably long in a burst-mode communication system. Furthermore, since the preambles of bursts are system overhead and do not convey useful data, use of lengthy preambles, for example, to allow for recovery of clock information, may unduly reduce communication bandwidth.